Fractal analysis, which other researchers have used previously to study the works of Jackson Pollock, characterizes patterns based on a single fractal dimension. That dimension indicates the relationship between of the edge of a pattern and its area. Multifractals, on the other hand, are potentially more powerful because they take into consideration the fact that a single pattern may have many fractal dimensions, depending on the size of a pattern region being analyzed.

The researchers also propose that edge multifractals, which characterize the shapes of the borders of colored regions rather than the locations of the colors on the canvas, appear to be promising tools for studying the aesthetic appeal of art works. Another technique called fractal reconstruction may eventually lead to a kind of fingerprint for artistic movements, but the researchers found the results too vague to be conclusive.

The last time you raised a glass of champagne in toast, you may have noticed the carbon dioxide bubbles in the glass rising to the surface in fine threads. If you were particularly observant, you may also have seen that threads are made of bubble groupings that change over time. Now, researchers from French and Brazilian universities have produced a new model that accounts for the patterns in strings of bubbles in champagne and other effervescent fluids.

Initially, champagne bubbles rise in strings made of bubble pairs. As time passes the groupings vary in number, and then turn into strings of three bubbles. Finally, they settle down into evenly spaced single bubbles.

The bubbles rise from nucleation points on the glass wall. The nucleation points are small defects in the glass that trap tiny vibrating pockets of carbon dioxide. Dissolved gas in the champagne gradually collects in a vibrating bubble inside the defect, causing it to grow and soon expel gas from the defect, forming another bubble that sticks to the outside of the defect. That bubble, in turn, grows as more dissolved carbon dioxide collects inside it and it eventually breaks free of the defect to rise through the champagne. Then the process begins again with a new bubble expelled from the defect, forming rising strings of tiny bubbles.

The variations in the sequences result from the interplay between the vibration of gas in the cavity and the rate at which bubbles grow outside of a cavity. These two rates depend on many factors such as champagne temperature and cavity size, but the only factor that changes over the same time scale as the change in the bubble patterns is the concentration of dissolved carbon dioxide.

According to the researchers, the work could be important in understanding bubbles formed of dissolved gasses in other situations, such as nitrogen bubbles that grow in the blood vessels of surfacing divers and can cause decompression sickness, and the explosive release of carbon dioxide gas from Cameroon's Lake Nyos that killed over 1800 people in 1986..

Highly symmetrical heartbeats, which look the same when run forward or backward in time, are one sign of an unhealthy heart. Researchers from Harvard Medical School and the University of Lisbon have developed a new index that provides a simple measure of the time reversibility of a heart rate signal. The index may lead to better models of heart rate control, and to new, easy methods for detecting heart problems. Previous efforts to look at time asymmetry in heartbeat patterns had considered only a single time scale, and often could not distinguish between sick and healthy people. The new approach provides a straightforward way to look at a range of time scales. Applying their method to heart rate data from healthy young people, healthy old people, and people with heart disease, the researchers found that heartbeat asymmetry is highest in young healthy subjects and declines with age or disease.

Kendra Rand, James Riordon, and Ernie Tretkoff contributed to these news tips.